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From Peter Joole <peter.jo...@gmail.com>
Subject NullPointerException when using HttpHead and Request/Response interceptors
Date Mon, 02 Apr 2012 20:24:12 GMT
Hi,

I have been using the HttpClient library for a couple of days now in my
project. I use the ThreadSafeClientConnManager() to get all my resources
and it works. I also use the example with the add request/response
interceptor to try to get the resources gzipped. However when I tried to
use a HttpHead instead of a HttpGet object I got a NullPointerException.

I can replicate the exception when using the ClientGZipContentCompression
example that can be found at the HttpClient examples. But instead of using
the HttpGet object I execute a HttpHead object. When I comment the
interceptor parts out, I don't get the exception.

So I was wondering if this is a bug or not?

This is the error stack trace I get when executing in netbeans:

Exception in thread "main" java.lang.NullPointerException
at
testhttphead.ClientGZipContentCompression$2.process(ClientGZipContentCompression.java:74)
at
org.apache.http.protocol.ImmutableHttpProcessor.process(ImmutableHttpProcessor.java:116)
at
org.apache.http.protocol.HttpRequestExecutor.postProcess(HttpRequestExecutor.java:342)
at
org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:472)
at
org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:820)
at
org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:754)
at
org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:732)
at
testhttphead.ClientGZipContentCompression.main(ClientGZipContentCompression.java:92)
Java Result: 1

Here is the code that gives me the error:

package testhttphead;

import java.io.IOException;
import java.io.InputStream;
import java.util.zip.GZIPInputStream;
import org.apache.http.*;
import org.apache.http.client.methods.HttpHead;
import org.apache.http.entity.HttpEntityWrapper;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.protocol.HttpContext;
import org.apache.http.util.EntityUtils;

/**
 * Demonstration of the use of protocol interceptors to transparently modify
 * properties of HTTP messages sent / received by the HTTP client.
 * <p/>
 * In this particular case HTTP client is made capable of transparent
content
 * GZIP compression by adding two protocol interceptors: a request
interceptor
 * that adds 'Accept-Encoding: gzip' header to all outgoing requests and a
 * response interceptor that automatically expands compressed response
entities
 * by wrapping them with a uncompressing decorator class. The use of
protocol
 * interceptors makes content compression completely transparent to the
consumer
 * of the {@link org.apache.http.client.HttpClient HttpClient} interface.
 */
public class ClientGZipContentCompression {

    public final static void main(String[] args) throws Exception {
        DefaultHttpClient httpclient = new DefaultHttpClient();

        try {
            httpclient.addRequestInterceptor(new HttpRequestInterceptor() {

                public void process(
                        final HttpRequest request,
                        final HttpContext context) throws HttpException,
IOException {
                    if (!request.containsHeader("Accept-Encoding")) {
                        request.addHeader("Accept-Encoding", "gzip");
                    }
                }
            });

            httpclient.addResponseInterceptor(new HttpResponseInterceptor()
{

                public void process(
                        final HttpResponse response,
                        final HttpContext context) throws HttpException,
IOException {
                    HttpEntity entity = response.getEntity();
                    Header ceheader = entity.getContentEncoding();
                    if (ceheader != null) {
                        HeaderElement[] codecs = ceheader.getElements();
                        for (int i = 0; i < codecs.length; i++) {
                            if
(codecs[i].getName().equalsIgnoreCase("gzip")) {
                                response.setEntity(
                                        new
GzipDecompressingEntity(response.getEntity()));
                                return;
                            }
                        }
                    }
                }
            });

            HttpHead httpHead = new HttpHead("http://www.howest.be");

            // Execute HTTP request
            System.out.println("executing request " + httpHead.getURI());
            HttpResponse response = httpclient.execute(httpHead);

            System.out.println("----------------------------------------");
            System.out.println(response.getStatusLine());
            System.out.println(response.getLastHeader("Content-Encoding"));
            System.out.println(response.getLastHeader("Content-Length"));
            System.out.println("----------------------------------------");

            HttpEntity entity = response.getEntity();

            if (entity != null) {
                String content = EntityUtils.toString(entity);
                System.out.println(content);

System.out.println("----------------------------------------");
                System.out.println("Uncompressed size: " +
content.length());
            }

        } finally {
            // When HttpClient instance is no longer needed,
            // shut down the connection manager to ensure
            // immediate deallocation of all system resources
            httpclient.getConnectionManager().shutdown();
        }
    }

    static class GzipDecompressingEntity extends HttpEntityWrapper {

        public GzipDecompressingEntity(final HttpEntity entity) {
            super(entity);
        }

        @Override
        public InputStream getContent()
                throws IOException, IllegalStateException {

            // the wrapped entity's getContent() decides about repeatability
            InputStream wrappedin = wrappedEntity.getContent();

            return new GZIPInputStream(wrappedin);
        }

        @Override
        public long getContentLength() {
            // length of ungzipped content is not known
            return -1;
        }
    }
}

With kind regards,

Peter

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